Just done a gearbox oil change on my Spider yesterday and took a few pictures to assist any other owners looking to do the same.
Finding the oil drain plug wasn't a problem (although I had to borrow a square allen key to undo it), however the gearbox oil filler cap is very tricky to spot - even looking at the pictures in the manual(s). It's green and hidden away so as to be very nearly impossible to see from above, and pretty un-obvious from below too!
Anyway, I should also note that although it's supposed to hold 3.1L, I think that the last 0.1L of my new oil just went straight onto the floor - so just buy 3L and that should be enough.
I used a two way pump syringe to draw up from the oil container and pump into the gearbox - making sure to push the pipe well into the hole to prevent oil from leaking out of the hole during filling.
Anyway, here are the pictures ...
- and that was nice! 
